1. Field of the Invention
The present invention relates to an integrally-molded ceramic alignment sleeve for use in an optical fiber connector for connecting optical fibers, which is used in optical communication systems and optical fiber sensors, and more particularly to an integrally-molded ceramic alignment sleeve with a high strength into which a ferrule can be precisely fitted with a good insertion feel. This invention also relates to a method of producing the above-mentioned integrally-molded ceramic alignment sleeve at low cost.
2. Discussion of Background
Conventionally, an optical fiber connector employing a zirconia ferrule is widely used in the field of optical communications. An integrally-molded split phosphor bronze or zirconia alignment sleeve is used as an adaptor for the above optical fiber connector. Particular attention is being paid to the split zirconia alignment sleeve because no metal powder is created during attachment or detachment of the ferrule, and excellent optical connection performance can be attained.
A conventional ceramic split alignment sleeve is in a cylindrical form as shown in FIG. 5, provided with a slit extending in the longitudinal direction of the sleeve. The inner surface of the sleeve is subjected to precision abrasion using diamond grain in such a way that the inner diameter of the sleeve is slightly smaller than the outer diameter of a ferrule to be inserted therein.
In the manufacture of the ceramic split alignment sleeve as shown in FIG. 5, however, the flowability of the diamond grain is poor because there is no relief on the inner surface of the sleeve. Furthermore, the area to be subjected to abrasion finishing is large, therefore the processability is poor and considerable time is expended in abrasion finishing. The problem also exists that the straightness of the split alignment sleeve in the longitudinal direction is not satisfactory because the flowability of the diamond grain is poor. Moreover, the variation of the necessary force to remove the ferrule from the thus prepared split sleeve after insertion is large. Therefore, when a split alignment sleeve with a good insertion feel is required, this variation causes the yield of finished products to worsen.
According to the technology disclosed in Japanese Laid-Open Patent Application 64-32210, by the provision of a convex portion with an arc-shaped cross-section extending in the longitudinal direction at three locations in the circumferential direction on the inner surface of a split alignment sleeve with a longitudinal slit, it is possible to steadily fit the ferrule into the split sleeve under pressure and secure the ferrule with stable pressure so that the force required to attach the ferrule to the sleeve or detach it therefrom can be considerably reduced. This kind of sleeve with convex portions is integrally molded from a metal or plastic. Alternatively, the sleeve body is formed from a plastic and then the convex portions are provided in the sleeve body by insert-molding of metal, ceramic or glass rods. In other words, the sleeve body itself and the convex portions with an arc-shaped cross-section are separate bodies.
In the above-mentioned Japanese Laid-Open Patent Application, there is no description that the sleeve body and the convex portions with the arc-shaped cross-section are integrally molded using a ceramic material. It is natural to assume that the internal processing of an integrally-molded ceramic product of a shape such as this is extremely difficult.
Also, since the convex portion is formed with an arc-shaped cross-section, the ferrule comes into line contact with the convex portion, so that the optical performance is ultimately governed by the roundness of the ferrule.
In addition, even with an integrally-molded ceramic alignment sleeve provided with convex portions, for instance, when the ferrule is inserted into the sleeve, stress concentration is produced at the section where each convex portion is connected to the internal surface of the sleeve body, and the mechanical strength of this type of sleeve becomes a problem.
Furthermore, when the sleeve body and the convex portions are separate members as disclosed in Japanese Laid-Open Patent Application 64-32210, a large number of manufacturing steps are required resulting in increased costs.